Text Msg

Mine sometimes refuses to send text messages as well. When I hit the 'send' icon it flickers but nothing happens. The message remains on the screen as if I am still writing it.

When this happens I reset it. Usually one reset is enough but sometimes I have to reset it two or three times for it to work. (By reset I mean sliding off the battery cover and putting it back)

About the other person not hearing you I had this problem also but found it was a very simple thing - something greasy (perhaps food or something) had gotten into the tiny hole at the bottom of the IPAQ (near the connector) and was totally blocking out the sound. I just cleaned out the opening and it then worked fine.
Also be careful not to cover it with your finger. That happens often to me. I have now learned to move my finger when someone tells me they cannot hear me.
If that doesn't solve the problem for you then I'm afraid it is a faulty microphone and will need to be repaired.